【作者】 高聿为；

【导师】 荆天辅； 王天生；

【作者基本信息】 燕山大学 ， 材料学， 2007， 博士

【摘要】 本论文研究目的是提出利用马氏体冷塑性变形及随后低温再结晶,以及马氏体温变形来制备纳米晶钢的方法,并对温变形力学行为、组织和性能的关系进行表征,为制备大块高性能超细晶/纳米晶钢铁材料提供参考。采用大压下量冷轧、温压缩和温轧方法,制备出了纳米多层钢板和亚微米级超细晶粒钢板。用Gleeble-3500热力模拟试验机进行了温压缩变形行为和拉伸性能测试,并用透射电镜（TEM）、扫描电镜（SEM）和X射线衍射仪（XRD）分析了微观组织。此外,还对马氏体温轧的可行性进行了分析。实验表明,15CrMnMoVA和Q235钢板条马氏体冷轧并低温退火,可以制备出纳米多层钢板,而且,通过调整冷轧压下量和退火工艺,可获得强度、塑性和韧性良好的配合。15CrMnMoVA钢经940℃淬火、65%冷轧及580℃×90min退火,得到了沿轧面近于平行排列的纳米层片晶粒,平均层片厚度约80nm。沿轧向的σ_b=1581MPa、σ_0.2=1567 MPa、δ=11.5%、α_k=55J·cm^-2、K_1C=110.7MPa·m^-1/2,其在5%NaCl溶液中的K1SSC=94.6 MPa·m^-1/2;Q235钢经940℃淬火、93.6%冷轧、350℃×60min退火,可获得平均晶粒尺寸为22.4nm、σ_b=1795MPa的纳米晶粒钢板。09MnNiDR钢板条马氏体组织400℃温轧及退火,可制备出纳米晶粒/亚微米晶粒钢板。温轧后经450℃×60min退火得到的平均晶粒尺寸为32.8nm,σ_b=1430MPa、σ_0.2=1008 MPa、δ=5.4%。钢的化学成分,特别是Mo和V,对纳米晶钢板热稳定性影响较大,Cr-Mo-V钢纳米层片组织的热稳定性最高,层片组织消失的温度高达650℃;其次为09MnNiDR钢,层片组织在500℃开始消失;Q235钢纳米层片组织热稳定性最低,层片组织在450℃开始消失。在本实验条件下,强度和硬度与晶粒尺寸之间在纳米尺度仍符合Hall-Petch关系。纳米多层钢板的耐蚀性高于供货状态,其主要原因是超均质和超细化。Q235纳米多层钢板在350℃×480min退火时钢板的耐蚀性最好,退火温度升高,耐蚀性变差。影响45钢马氏体温变形流变行为的主要因素是化学成分、变形温度、应变速率和应变量,其中变形温度影响最大。550⁷00℃变形,马氏体组织的流变应力与F+P组织相当,加工软化率和应变速率敏感性指数都大于F+P组织,马氏体的表观变形激活能为370.3 kJ·mol-1,F+P的表观变形激活能为355.6 kJ·mol-1,得到了它们的温变形方程和变形抗力与Z参数间的关系。马氏体550⁷00℃、0.01s-1变形后的组织由平均晶粒尺寸为200nm～1.73μm的等轴状铁素体和平均尺寸为32nm～62nm颗粒状碳化物组成。马氏体温变形组织室温拉伸性能优于F+P温变形组织。根据现行铁素体轧制理论,以及本文中碳钢马氏体与F+P温变形行为和组织演化的实验结果,可以证明,马氏体温加工用于超细晶粒钢生产是可行的,提出了马氏体温加工制备超细晶粒钢的新方案。更多还原

【Abstract】 The aim of this dissertation is to present the methods for the preparation of nanograined steels, one is martensite plastic deformation and subsequent recrystallization; other is martensite warm deformation. In addition, the warm deformation behavior and the relationship between the microstrcture and the property were characterized. This will provide a reference to fabrication of high-performane bulk nano-/ultrafine-grained steels. Nano-multilayer/submicro-grained steels were successfully prepared by using the heavy cold rolling, warm deformation and warm rolling. The warm compressive deformation behavior and the tensile properties were studied on Gleeble-3500 thermo-mechanical simulator. The microstructures was examined by means of transmission electron microscopy （TEM）, scanning electron microscopy （SEM） and X-ray diffractometry （XRD）. The feasibility of martensite warm rolling was also discussed.Experimental results show that nano-multilayer 15CrMnMoVA and Q235 steels can be prepared by the annealing of the lath martensite. Moreover, good combination of strength, plasticity and toughness can be achieved by modifying reduction and annealing parameter. For 15CrMnMoVA steel, parallel arrangemnt nanoscale lamella with average thickness of about 80 nm can be obtained in 15CrMnMoVA steel by quenching at 940°C, and cold rolling in reduction of 65%, and then annealing at 580°C for 90 min. The properties along rolling direction are as follows:σ_b=1581 MPa,σ_0.2=1567 MPa,δ=11.5%,α_k=55J·cm^-2, K_1C=110.7MPa·m^-1/2, and K_1SSC=94.6 MPa·m^-1/2 in 5%NaCl solution. For Q235 steel, nanograins with size of ²2.4 nm can be obtained by quenching at 940°C, and cold rolling in reduction of 93.6%, and then annealing at 350°C for 60 min, andσb reaches 1795 MPa. For 09MnNiDR steel, nano-/submicro-grained steel plate can be fabricated by warm rolling of martensite at 400°C and annealing. Nanograins with the average size of ³2.8 nm can be attained by annealing at 450°C for 60 min after the warm rolling. The tensile properties areσ_b=1430 MPa,σ_0.2=1008 MPa,δ=5.4%.The chemical composition of steels, especially Mo and V, has a great effect on thermal stability of the nanograined steels. The thermal stability is the highest for Cr-Mo-V steel, for which the lamella structures start to change when the temperature is up to 650°C; and the secondary for 09MnNiDR, for which the lamella structures start to change when the temperature is 500°C; the lowest for Q235 steel, for which the lamella structures start to change when the temperature reaches just to 450°C. Under the present experiment condition, the dependences of grain size on strength and hardness agree with Hall-Petch correlation. The corrosion resistance of the nano-multilayer steels is higher than that of the as received, which is mainly attributed to superhomogeneous and ultrfinement. The corrosion resistance of nano-multilayer Q235 steel annealed at 350°C for 480 min is better than that annealed under other parameters. The corrosion resistance decreases with annealing temperature increases.The main effect factors on flow behavior of warm deformation of martensitic 45 steel are chemical composition, deformation temperature, strain rate and strain, and the deformation temperature has the strongest effect on the flow stress. During deformation in the temperature ranged 550 to700°C, the flow stress of martensite is approximately equal to that of F+P, the working softening rate and strain rate sensitivity index for martensite are more than those for F+P. The appearance activation energies of the warm deformation of martensite and F+P are 370.3 and 355.6 kJ?mol-1, respectively. The warm deformation equations and the relationships between the deformation resistance and Z parameter of 45 steel with martensite and F+P were educed. The microstructure of martensitic 45 steel deformed in 550⁷00°C at 0.01 s-1 is composed of equiaxial ferritic grains with the mean size of 200nm¹.73μm and the granular cementite with the mean size of 32nm⁶2nm. The room-temperature tensile properties of warm deformed 45 steel with starting microstructure of martensite excel those of F+P.Based on actual ferrite rolling theory and the warm deformation behavior and microstructure evolution of martensitic and F+P microstructural medium carbon steel, it is demonstrated that the production of ultrafine grained steels by using warm deformation of martensite is feasible. The new route to prepare ultrafine grained steels by warm deformation of martensite was presented.更多还原